【发布时间】：2015-03-07 00:19:47
【问题描述】：
我想为我冗长的问题道歉，这只是我第二次使用这个网站。在不久的将来，我会确保我的问题有条不紊地综合起来。
我正在编写一个 n x m 矩阵类，其中包括重载乘法。目前，仅当第一个输入矩阵的列与第二个矩阵的行匹配时，代码才适用于 n x n 和 n x m 矩阵乘法，而不是相反。比如：
a1 a2 * b1
b2
这可行（抱歉，我没有足够的声誉点来发布图片，但可以将其视为 1x2 矩阵 * 2x1 矩阵）。
a1 * b1 b2
a2
但是这种类型的输入不起作用。
我的矩阵类由以下给出：
#include<iostream>
#include <stdlib.h>
using namespace std;
class dymatrix
{
friend ostream & operator << (ostream &os, const dymatrix &om);
friend istream & operator >> (istream &is, dymatrix &om);
private:
int rows;
int columns;
double *matrix;
public:
dymatrix(){cout<<"Default constructor called"<<endl; columns = 0; rows=0; matrix=0;}
~dymatrix(){cout<<"Destructor called"<<endl;delete[] matrix;}
dymatrix(int inrows, int incolumns) //Parametrised objects, matrix database is defined here to store data.
{
rows = inrows;
columns = incolumns;
matrix = new double [inrows*incolumns];
for (int i=0; i<inrows*incolumns; i++)
{
matrix[i]=0;
}
}
int lengthr() const {return rows;} //Returns number of rows.
int lengthc() const {return columns;} //Return number of columns.
dymatrix &operator=( dymatrix &arr); //This is the assignment member function.
dymatrix(dymatrix&); //This is the deep copy member function.
dymatrix operator*(const dymatrix& arr)const ; //Overloading "*" operator.
double & operator[](const int n) //Overloading "[]" operator, this is important !!!
{
if(n<0 || n>=rows*columns)
{
cout<<"Error: trying to access matrix element out of bounds"<<endl;
exit(1);
}
return matrix[n];
}
int index(int j, int i) const //This member function returns the position of each index.
{
if (j > 0 && j <=rows && i > 0 && i <=columns)
{
//cout<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl;
return (i-1)+(j-1)*columns;
}
else {cout<<"Error, out of range"<<endl<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl; exit (1);}
}
double & operator()(int j, int i) const {return matrix[index(j,i)];} //The operator () returns the position of j and i in 1D array.
}; //Class End.
“index”成员函数将矩阵内每个元素的位置返回到一维数组中：
int index(int j, int i) const //This member function returns the position of each index.
{
if (j > 0 && j <=rows && i > 0 && i <=columns)
{
//cout<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl;
return (i-1)+(j-1)*columns;
}
else {cout<<"Error, out of range"<<endl<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl; exit (1);}
}
double & operator()(int j, int i) const {return matrix[index(j,i)];} //The operator () returns the position of j and i in 1D array.
这是我在类外重载 乘法 " * " 运算符的部分：
dymatrix dymatrix:: operator * (const dymatrix &arr) const //Overloading "*" operator.
{
if (columns != arr.rows)
{
cerr<<"SIZE DO NOT MATCH, YOU FAIL"<<endl; exit(1);
}
dymatrix new_matrix(rows,arr.columns);
for (int j = 1; j <= rows; j++)
{
for (int i = 1; i <= arr.columns; i++)
{
for (int k = 1; k <= columns; k++)
{
new_matrix.matrix[index(j,i)]= new_matrix.matrix[index(j,i)]+ matrix[index(j,k)]*arr(k,i);
cout<<"new_matrix = "<<new_matrix<<endl<<endl;
}
}
}
return new_matrix;
}
这里给出了int main：
int main()
{
dymatrix a1;
cin >> a1; //Define the rows of the matrix
cout << a1<<endl<<endl;
dymatrix a2;
cin >> a2;
cout << a2<<endl<<endl;
dymatrix resu_a3;
resu_a3 = a1*a2;
cout<<"Multiplication = "<<resu_a3<<endl;
return 0;
}
所以我运行代码后得到的错误消息是我自己在“index”成员函数中写的：
“错误，超出范围”。
此错误消息表明 i 和 j 分别小于 0 或大于现有列数和行数，我不明白为什么会这样。
我的完整代码在这里给出：
#include<iostream>
#include <stdlib.h>
using namespace std;
class dymatrix
{
friend ostream & operator << (ostream &os, const dymatrix &om);
friend istream & operator >> (istream &is, dymatrix &om);
private:
int rows;
int columns;
double *matrix;
public:
dymatrix(){cout<<"Default constructor called"<<endl; columns = 0; rows=0; matrix=0;}
~dymatrix(){cout<<"Destructor called"<<endl;delete[] matrix;}
dymatrix(int inrows, int incolumns) //Parametrised objects, matrix database is defined here to store data.
{
rows = inrows;
columns = incolumns;
matrix = new double [inrows*incolumns];
for (int i=0; i<inrows*incolumns; i++)
{
matrix[i]=0;
}
}
int lengthr() const {return rows;} //Returns number of rows.
int lengthc() const {return columns;} //Return number of columns.
dymatrix &operator=( dymatrix &arr); //This is the assignment member function.
dymatrix(dymatrix&); //This is the deep copy member function.
dymatrix operator*(const dymatrix& arr)const ; //Overloading "*" operator.
double & operator[](const int n) //Overloading "[]" operator, this is important !!!
{
if(n<0 || n>=rows*columns)
{
cout<<"Error: trying to access matrix element out of bounds"<<endl;
exit(1);
}
return matrix[n];
}
int index(int j, int i) const //This member function returns the position of each index.
{
if (j > 0 && j <=rows && i > 0 && i <=columns)
{
//cout<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl;
return (i-1)+(j-1)*columns;
}
else {cout<<"Error, out of range"<<endl<<"i is "<<i<<" j is "<<j<<endl<<endl<<"row is "<<rows<<" columns is "<<columns<<endl; exit (1);}
}
double & operator()(int j, int i) const {return matrix[index(j,i)];} //The operator () returns the position of j and i in 1D array.
}; //Class End.
dymatrix::dymatrix(dymatrix &arr) //This is the copy constructor for deep copying.
{
matrix = 0; rows = arr.lengthr(); columns = arr.lengthc();
if (rows*columns >0)
{
matrix = new double [rows*columns];
for (int i =0; i < rows*columns; i++)
{
matrix[i] = arr[i];
}
}
}
dymatrix & dymatrix ::operator = (dymatrix &arr)
{
if(&arr == this) return *this; // no self assignment
delete[] matrix; matrix=0; rows=columns=0;
rows=arr.lengthr();
columns = arr.lengthc();
if(rows*columns>0)
{
matrix=new double[rows*columns];
// Copy values into new array
for(int i=0;i<rows*columns;i++) matrix[i] = arr[i];
}
return *this; // Special pointer!!
}
istream & operator >> (istream &is, dymatrix &om) //Overloading ">>" operator here to
{
cout<<"Please enter the number of rows you want"<<endl;
is >> om.rows; //Inputting number of rows.
cout<<"Enter the number of columns you want"<<endl;
is >> om.columns; //Inputting number of columns.
cout<<"Enter matrix"<<endl;
om.matrix = new double [om.rows*om.columns]; //Making a dynamic array here to put the data in.
for (int j = 1; j <= om.rows; j++)
{
for (int i = 1; i <= om.columns; i++)
{
is >> om.matrix[om.index(j,i)]; //Putting in the data into this dynamic array for each element.
}
}
return is;
}
ostream & operator << (ostream &os, const dymatrix &om) //To output the matrix in an standard matrix way
{
for(int j= 1; j<=om.rows; j++)
{
os<<endl<<endl;
for (int i = 1; i <=om.columns;i++)
{
os << om.matrix[om.index(j,i)]<<"\t"; //Similar method used in istream.
}
}
return os;
}
dymatrix dymatrix:: operator * (const dymatrix &arr) const //Overloading "*" operator.
{
if (columns != arr.rows)
{
cerr<<"SIZE DO NOT MATCH, YOU FAIL"<<endl; exit(1);
}
dymatrix new_matrix(rows,arr.columns);
for (int j = 1; j <= rows; j++)
{
for (int i = 1; i <= arr.columns; i++)
{
for (int k = 1; k <= columns; k++)
{
new_matrix.matrix[index(j,i)]= new_matrix.matrix[index(j,i)]+ matrix[index(j,k)]*arr(k,i);
cout<<"new_matrix = "<<new_matrix<<endl<<endl;
cout<<"k "<<k<<endl<<" arr.columns is "<<arr.columns<<endl<<"columns is "<<columns<<endl<<endl;
}
}
}
return new_matrix;
}
int main()
{
dymatrix a1;
cin >> a1; //Define the rows of the matrix
cout << a1<<endl<<endl;
dymatrix a2;
cin >> a2;
cout << a2<<endl<<endl;
dymatrix resu_a3;
resu_a3 = a1*a2;
cout<<"Multiplication = "<<resu_a3<<endl;
return 0;
}
【问题讨论】：
-
Fyi
dymatrix &operator=( dymatrix &arr);不高兴当分配的右侧是临时的，它在您的resu_a3 = a1*a2;语句中。除非您使用的编译器支持对 temps 的非标准非常量引用（例如：MS），否则它将无法编译。前任;这不会用 clang 3.5 编译。 -
谢谢，我使用的编译器工作正常。我已将其更改为
dymatrix &operator=( dymatrix arr);，但同样的问题仍然存在。 -
哦，伙计....请帮我们大家一个忙，学习合成；如果仅仅阅读问题需要 15 分钟，那么您不太可能得到任何帮助......
-
对此我深表歉意，这是我第二次尝试在这个网站上提问。建议指出，我将学会综合我在不久的将来提出的任何问题。